TL;DR
- Single garage: 1 day
- Double garage: 1–2 days
- Small extension: 1–2 days
- Large extension: 2–3 days
- Porch: Half day to 1 day
- Bay window: Half day
- Most domestic flat roofs complete within 1–2 working days
- Factors extending time: deck repairs, complex shapes, multiple penetrations, access difficulties, weather delays
- EPDM rubber roofing installs faster than felt or fibreglass alternatives
- Prepare for installation by clearing the area below and ensuring access—your preparation time is minimal
Planning around a flat roof installation requires knowing how long the work will take. Whether you need to arrange time off work, move vehicles, or coordinate with other tradespeople, realistic timescales help you prepare properly.
The good news: most domestic flat roofing projects complete within one to two days. Larger or more complex jobs may take longer, but flat roofing is generally quicker than many homeowners expect.
This guide provides realistic installation timescales for every common flat roof project, explains what affects duration, and helps you plan effectively.
Quick Reference: Installation Times
Here’s how long typical flat roof installations take:
| Project Type | Typical Duration |
|---|---|
| Bay window roof | Half day |
| Small porch (under 5m²) | Half day |
| Large porch (5–10m²) | Half day to 1 day |
| Single garage | 1 day |
| Double garage | 1–2 days |
| Small extension (10–20m²) | 1–2 days |
| Medium extension (20–35m²) | 2–3 days |
| Large extension (35–50m²) | 3–4 days |
| Dormer roof | Half day to 1 day |
| Garden room (15–25m²) | 1–2 days |
| Conservatory conversion | 2–4 days |
These timescales assume straightforward conditions. Various factors can extend duration.
Detailed Timescales by Project Type
Let’s break down what’s involved in each project and why timing varies.
Bay Window Roofs
Typical duration: Half day (3–4 hours)
What’s involved:
- Access setup
- Old covering removal
- Deck check
- New membrane installation
- Edge details
- Cleanup
Why it’s quick: Small area (typically 2–4m²), often accessible from ladder, limited complexity.
What might extend it: Difficult access, significant deck damage, complex shape requiring extra detailing.
Porch Roofs
Small porch (under 5m²): Half day
Large porch (5–10m²): Half day to 1 day
What’s involved:
- Setup and preparation
- Existing covering removal
- Deck inspection and any repairs
- Insulation if required
- Membrane installation
- Edge and wall junction details
- Cleanup and handover
Why porches are relatively quick: Compact area, usually ground-level access, typically simple rectangular shape.
What might extend it: Integration with house structure requiring careful junction work, poor original construction requiring remediation.
Single Garage Roofs
Typical duration: 1 day
Detailed breakdown:
| Stage | Duration |
|---|---|
| Setup and preparation | 30 minutes |
| Old covering removal | 1–2 hours |
| Deck inspection | 30 minutes |
| Deck repairs (if needed) | 30 minutes–2 hours |
| Insulation installation | 1 hour |
| Membrane preparation | 30 minutes |
| Adhesive application | 1 hour |
| Membrane bonding | 45 minutes |
| Edge details | 1–1.5 hours |
| Penetration sealing | 30 minutes |
| Final inspection and cleanup | 30 minutes |
| Total | 7–10 hours |
Why a day works: Single garage roofs (typically 15–20m²) are the perfect size for a day’s work—large enough to require systematic approach but compact enough to complete.
What might extend it: Extensive deck damage, awkward access, multiple penetrations, complex shapes.
Double Garage Roofs
Typical duration: 1–2 days
Why longer than single: Approximately double the area means more material to handle, more adhesive to apply, longer edge perimeter.
Breakdown:
- Day 1: Setup, removal, deck work, insulation, potentially begin membrane work
- Day 2 (if needed): Complete membrane, all details, cleanup
When it’s 1 day: Sound deck, simple shape, experienced team, good conditions.
When it’s 2 days: Deck repairs needed, complex shapes, multiple penetrations, larger crews completing methodically.
Extension Roofs
Extensions vary more in duration due to greater size variation and complexity.
Small extension (10–20m²): 1–2 days
Medium extension (20–35m²): 2–3 days
Large extension (35–50m²): 3–4 days
What affects extension timing:
| Factor | Impact |
|---|---|
| Simple rectangle | Baseline timing |
| L-shape | Add half day |
| Multiple penetrations (skylights, vents) | Add 1–2 hours per penetration |
| Complex wall junctions | Add 2–4 hours |
| Significant deck repairs | Add half to full day |
Extension-specific considerations:
- Integration with house requires careful junction work
- Building regulations compliance may require specific insulation
- Often coordinated with other trades in new-build situations
Dormer Roofs
Typical duration: Half day to 1 day (roofing work only)
Breakdown:
- Access establishment: 30 minutes (if scaffold in place)
- Old covering removal: 1 hour
- Deck check and repairs: 30 minutes–1 hour
- Membrane installation: 1–2 hours
- Tile integration/flashing: 1–2 hours
- Cleanup: 30 minutes
Access factor: If scaffolding must be erected specifically for dormer work, add time and cost. If scaffold exists from loft conversion, access is already handled.
Why dormers can be quick: Small area (typically 5–10m²). Why they can take longer: Height access, integration with surrounding tiles requires care.
Garden Rooms and Outbuildings
Small outbuilding (under 10m²): Half day to 1 day
Garden room (15–25m²): 1–2 days
Large garden building (25m²+): 2–3 days
Factors:
- New builds typically faster than replacements (no removal phase)
- Quality garden rooms warrant careful attention
- Insulation requirements extend time if included
Conservatory Roof Conversions
Typical duration: 2–4 days
Why longer: Conservatory conversions involve more than just membrane installation:
- Structural assessment
- Existing roof removal
- New structure installation
- Insulation
- Membrane installation
- Internal ceiling
- Potentially electrical work
This isn’t simple re-roofing—it’s construction work that happens to end with flat roofing.
Factors That Affect Installation Time
Understanding what extends (or shortens) duration helps with planning.
Deck Condition
Impact: Variable—can add hours to a full day
Best case: Existing deck is sound. Remove old covering, brief inspection, proceed to new installation.
Worse case: Significant rot or damage from previous leaks. Boards must be replaced before roofing can proceed.
| Deck Condition | Time Impact |
|---|---|
| Sound (no repairs) | None |
| Minor spot repairs | Add 30 minutes–1 hour |
| Partial board replacement | Add 1–3 hours |
| Extensive replacement | Add half to full day |
The unknown factor: Deck condition often isn’t fully known until old covering is removed. Quality installers discuss this possibility upfront.
Roof Complexity
Impact: Moderate to significant
Simple shapes (rectangles) are fastest. Every angle, corner, and junction requires additional detail work.
| Shape Factor | Time Impact |
|---|---|
| Simple rectangle | Baseline |
| L-shape | Add 10–20% |
| U-shape or wraparound | Add 20–30% |
| Multiple levels | Add 25–40% |
| Unusual angles | Add 15–25% |
Penetrations
Impact: Moderate
Every pipe, vent, skylight, or feature passing through the roof requires sealing.
| Penetration Type | Time to Seal |
|---|---|
| Simple pipe (SVP, vent) | 15–30 minutes |
| Extraction duct | 20–30 minutes |
| Skylight/roof window | 30–60 minutes |
| Roof lantern | 45–90 minutes |
| Multiple pipes clustered | 20–40 minutes |
A roof with five penetrations versus one might add 1–2 hours to the project.
Access
Impact: Low to moderate
| Access Situation | Time Impact |
|---|---|
| Ground level, clear | None |
| Scaffold required | Setup time + cost |
| Materials through house | Add 30–60 minutes |
| Restricted vehicle access | Add 30–60 minutes |
| Height/roof access needed | Variable |
Weather
Impact: Can be significant
EPDM installation requires:
- Dry conditions (no rain)
- Temperature above 5°C
- Manageable wind
What happens with weather:
- Forecast rain: Work may be rescheduled
- Rain during work: Pause until dry
- Temperature drop: May pause until warmer
- High wind: Large membrane handling becomes difficult
Planning implication: Built in flexibility. A “1 day” job might span 2 calendar days if weather interrupts.
New Installation vs Replacement
Impact: Replacement adds 1–3 hours
| Project Type | Time Comparison |
|---|---|
| New installation (bare deck) | Baseline |
| Replacement (remove existing) | Add 1–3 hours |
Replacement projects include removal and disposal of existing materials before new installation can begin.
Team Size
Impact: Variable
Most domestic flat roofing uses 1–2 person teams. Larger commercial projects might use larger crews.
| Crew Size | Typical Projects |
|---|---|
| 1 person | Very small roofs, simple jobs |
| 2 people | Most domestic work |
| 3+ people | Large commercial, tight deadlines |
Larger crews don’t always mean proportionally faster work—there are practical limits to how many people can work effectively on a roof simultaneously.
Material Comparison: Installation Speed
Different flat roofing materials install at different speeds.
EPDM Rubber Roofing
Speed: Fastest for most applications
Why:
- Single large sheets cover quickly
- Adhesive bonding is straightforward
- No heat or special equipment required
- Details are relatively simple
Felt Roofing
Speed: Moderate
Why slower than EPDM:
- Multiple layers required
- Torch application takes time
- More seams to seal
- Heat work requires care
Typical time difference: Felt takes 10–20% longer than EPDM for equivalent area.
Fibreglass (GRP)
Speed: Slowest
Why slower:
- Multiple coats of resin required
- Curing time between stages
- Weather-sensitive application
- More labour-intensive process
Typical time difference: GRP can take 30–50% longer than EPDM.
Material Speed Summary
| Material | Relative Speed | 20m² Roof Example |
|---|---|---|
| EPDM | Fastest | 1 day |
| Felt | Moderate | 1–1.5 days |
| GRP | Slowest | 1.5–2 days |
Planning Around Installation
How to prepare for flat roof installation timing.
Before Installation Day
One week before:
- Confirm date with installer
- Check weather forecast
- Plan access arrangements
- Notify neighbours if appropriate
Day before:
- Clear area beneath roof
- Move vehicles that might be in the way
- Ensure installer has access to property
- Confirm contact arrangements
On Installation Day
Early morning: Installers arrive, unload materials, begin setup.
During day: Steady work progress. You don’t need to supervise, but being available for occasional questions helps.
End of day: Site cleared, brief summary of work completed (or progress if multi-day).
What You Need to Arrange
| Arrangement | Duration Needed |
|---|---|
| Clear garage/area | 30 minutes day before |
| Move vehicles | 5 minutes |
| Be available for access | Start and end of day |
| Provide water/facilities | As needed |
Your preparation time is minimal—professionals handle the work.
Time Off Work?
For most projects: Not essential. You don’t need to supervise.
When it helps:
- If access requires your presence
- If decisions might be needed (unexpected issues)
- For handover at completion
Practical approach: Be contactable during installation. Physical presence isn’t required throughout.
Regional Considerations: South Wales
Local factors affecting installation timing.
Weather in South Wales
Our region’s wet climate means:
- More careful weather scheduling
- Flexibility built into timelines
- Occasional weather delays accepted as normal
Across South Wales—whether in Cardiff, Swansea, Merthyr Tydfil, Aberdare, or surrounding valleys—experienced installers understand local weather patterns and schedule accordingly.
Seasonal Considerations
| Season | Considerations |
|---|---|
| Spring | Variable weather; good working periods |
| Summer | Best conditions; busiest period |
| Autumn | Shorter days; weather becomes less reliable |
| Winter | Possible during dry, mild spells; requires flexibility |
Year-round installation: Quality installers work throughout the year, scheduling around weather windows.
What If It Takes Longer Than Expected?
Sometimes installations extend beyond planned duration.
Common Reasons
- Deck damage discovered after removal
- Weather interruption
- Unexpected complexity
- Supply issues (rare)
How Good Installers Handle Extensions
Communication: You’re informed promptly with clear explanation.
No surprise costs: Deck repairs are quoted at the time of discovery, not as surprises at completion.
Professional approach: Work continues systematically; rushing compromises quality.
Your Expectations
Quality over speed: A roof taking an extra half-day for proper attention is better than a rushed job that fails in years.
Weather delays are not failures: Pausing for rain is professional practice, not incompetence.
Frequently Asked Questions
Can flat roofing be installed in one day?
Yes, often. Single garages, porches, and small extensions routinely complete in one day. Larger projects may need more time.
What’s the quickest flat roof installation?
Bay window or small porch: Half a day. These small, simple roofs are the fastest projects.
Will bad weather delay my installation?
Possibly. EPDM needs dry conditions. Quality installers reschedule or pause rather than compromise work. Brief delays are better than premature failure.
Should I take time off work for installation?
Usually not necessary. Being contactable is enough. You don’t need to supervise.
How far in advance should I book?
2–4 weeks typically, though this varies seasonally. Summer is busiest. Winter may have shorter lead times.
Can I use the space beneath while work happens?
Garage/extension contents: Usually fine to remain, but cover anything directly beneath if concerned about debris.
Living spaces: Normal use continues. Interior impact is minimal.
Summary: Realistic Timescales for Your Project
Most domestic flat roofing completes faster than homeowners expect:
| Project | Typical Time |
|---|---|
| Small projects (porches, bays) | Half day |
| Garages | 1 day |
| Extensions | 1–3 days |
| Large or complex projects | 3–4 days |
Planning tips:
- Confirm timescale with your installer
- Build in weather flexibility
- Clear access and preparation takes minimal time
- Quality matters more than speed
Understanding realistic timescales helps you plan effectively without unnecessary concern. Professional flat roof installation is efficient, systematic, and typically straightforward.
Get Your Flat Roof Installed Efficiently
At M&J Roofing, we provide clear timescales for every flat roofing project. We’ll tell you exactly how long your installation should take, explain any factors that might affect duration, and keep you informed throughout.
Ready to discuss your project? Contact us for a quotation including realistic timescales tailored to your specific requirements.
